I just noticed (on a hot day) that my 2004 LS430 has an intermittent hissing sound from the A/C. In the olden days it was a sign that it needed freon.

I am still under warranty (but not for long) and will have the dealer look at it so I am not too concerned. But just curious if any of you have any idea what it is. I'd hate for the dealer to say there is little to nothing wrong then go out of warranty and require a compressor or something expensive.

Also, I will be at about 50,000 miles as the warranty expires. What can I expect over the next 2-3 years (12-15K/year) in the way of major repairs not covered by warranty?

 

Do you notice that the hissing increases with deceleration and decreases with acceleration? This is generally a sign of a crack/leak in your vacuum lines. The vacuum lines control (at least in my current car) the actuators(spelling?) that change where the air comes from.

 

No, it doesn't seem to be like that. It seems to just cycle "hissss" on and off maybe with the compressor?

 

Usually hissing from the AC system means air in the system. Likely from some kind of leak. has your Ac system been getting "weaker"? Make sure you sit there with the mechanic and make sure they hear it and make sure they document it. If you bring the problem to their attention and they fiddle around until warranty is out, you have proof of the problem.

 

Yeah, I do want to at least document the problem (by bringing it in for a warranty attempt at repair). It was 93 and humid yesterday here and the A/C was FREEZING. So I don't notice any weakness.

 

My minivan started making that noise. Same as your description. Goes off and on with the compressor. After about 1.5 years, the AC was noticeably weaker. Fixed it after discovering a small leak and recharging the system.